Steerable Capsule Apparatus and Method

ABSTRACT

A capsule includes a main body with at least one tail connected to the main body. At least two coils are disposed on each tail such that the coils are responsive to a magnetic field interacting with the coils such that a force is exerted on the tail. The capsule is controlled through application of a varying magnetic field with a constant current in the coils and/or by providing varying a current in the coils that interact with a constant magnetic field. The capsule can be disposed in a cavity, and the magnetic field can be provided from outside the cavity to affect movement of the capsule. An MRI device can be configured to control and image the capsule.

RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional application No.60/938,909, filed May 18, 2007, which is incorporated by reference inits entirety herein.

TECHNICAL FIELD

This invention relates generally to capsules or pills for use in a bodyfor medical purposes and more specifically to steerable such capsules orpills.

BACKGROUND

Various methods of direct exploration of body cavities are known formedical diagnosis and treatment. One example is the capsule endoscope,which has been used in the diagnosis of small intestine bleeding anddetection of Crohn's Disease, Celiac disease, and other malabsorptiondisorders, as well as benign and malignant tumors of the smallintestine. The capsule endoscope includes essentially a camera in a pillform that the subject swallows. As the capsule passes through thedigestive tract of the subject, the camera captures many pictures of thetract. After the capsule passes out of the subject, the pictures areretrieved and analyzed. The capsule endoscope can reach areas of thesmall intestine that a conventional endoscope cannot.

Although capsule endoscopy is an improved technique for detectingsources of small bowel bleeding, it does not achieve 100% detection. Thecapsule is purely diagnostic and cannot be used to take biopsies, applytherapy, or mark abnormalities for surgery. Moreover, the capsule cannotbe controlled once it has been ingested, so that its progress cannot beslowed to better visualize a suspicious abnormality.

Swimming capsules are an advanced version of capsule (also called aswimming micro-robot) that can be actively positioned by propulsion. Onesuch device included piezoelectric actuators based on ionic conductingpolymer film. A later similar device included a symmetrical structurewith four fins that allowed the micro-robot to turn as well as swim.Changing the frequency of one of the two piezoelectric actuators enabledturning.

Another known approach includes a micro-robot powered by a staticmagnetic field. The swimming mechanism in this approach included a helixtail in an alternating magnet field generated by a physically rotatingpermanent magnet. The micro-robot was made of a spiral copper wire and aSmCo permanent magnet attached to its tip. By applying an externalalternating magnetic field, magnetic torque can be created at the tip ofthe spiral copper wire. Alternatively, an electrically generatedmagnetic field could be used.

Yet another known approach includes using a magnetic actuator composedof a magnet and spiral structure that can be moved wirelessly byapplying an external magnetic field. The magnetic actuator in thisapproach was composed of a capsule dummy, a permanent magnet inside thecapsule, and a spiral structure. The actuator was rotated and propelledwirelessly by applying an external rotational magnetic field. Thecapsule, however, can only move forwards or backwards in thegastro-intestinal (“GI”) tract and depends on the assumption that thecapsule always has contact with the GI tract. Thus, three-dimensionalposition and orientation control of the capsule is not possible,prohibiting the range of its application in GI tract.

Another disadvantage to previous approaches is that the location of theprevious swimming micro-robots could not be determined duringexamination. Magnetic resonance imaging (“MRI”), a minimally invasiveyet comprehensive imaging technology, may provide this capability;however, the above approaches used ferro-magnetic materials such as apermanent magnet in the capsule and rotating local magnetic fields togenerate propulsion. Such propulsive mechanisms cannot be combined withMRI due to the interaction of the ferro-magnetic material with an MRI'smagnetic field. It is also difficult to place an additional set ofmagnetic field generators inside an MRI device and also virtually anyother medical imaging device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above needs are at least partially met through provision of thesteerable capsule apparatus and method described in the followingdetailed description, particularly when studied in conjunction with thedrawings, wherein:

FIG. 1 comprises a perspective view of an example one tail capsule asconfigured in accordance with various embodiments of the invention;

FIG. 2 comprises a perspective views of two example coils with anindication of the current and forces for the coils as configured inaccordance with various embodiments of the invention;

FIG. 3 comprises a perspective view of an example three-tail capsule asconfigured in accordance with various embodiments of the invention;

FIG. 4 comprises a graphic illustration of the motion of an examplecapsule tail by sequel snapshots of a tail simulation at ten differenttime points I through X;

FIG. 5 comprises a perspective view of an example capsule with tailsproximate to the capsule main body as configured in accordance withvarious embodiments of the invention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions and/or relative positioningof some of the elements in the figures may be exaggerated relative toother elements to help to improve understanding of various embodimentsof the present invention. Also, common but well-understood elements thatare useful or necessary in a commercially feasible embodiment are oftennot depicted in order to facilitate a less obstructed view of thesevarious embodiments of the present invention. It will further beappreciated that certain actions and/or steps may be described ordepicted in a particular order of occurrence while those skilled in theart will understand that such specificity with respect to sequence isnot actually required. It will also be understood that the terms andexpressions used herein have the ordinary technical meaning as isaccorded to such terms and expressions by persons skilled in thetechnical field as set forth above except where different specificmeanings have otherwise been set forth herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Generally speaking, pursuant to these various embodiments, a capsulegenerally includes a main body with at least one tail connected to themain body. The main body may include any of several elements useful invarious medical applications. The tail(s) may extend from the main bodyor be positions near and/or along the main body. At least two coils aredisposed on each tail such that the coils are responsive to a magneticfield interacting with the coils such that a force is exerted on thetail. Typically, each coil includes a number of turns and a surface areasuch that each coil has a resonant frequency. The capsule may becontrolled through application of a magnetic field. The capsule can bedisposed in a cavity, and the magnetic field can be provided fromoutside the cavity to affect movement of the capsule.

So configured, the capsule can be steered through a body cavity that canbe simultaneously imaged by, for example, an MRI device because thecapsule does not require ferro-magnetic elements to be incorporatedwithin its body. Advantageously, the capsule can be controlled thoughthe use of magnetic field generators inherently available in a typicalMRI device. Accordingly, the capsule can be imaged at the same time asthe cavity, and an image of the cavity can be marked with the capsulelocation. In this manner, areas of interest may be marked for follow uptreatment or investigation. Similarly, the capsule can be directed to anarea of interest discovered during an imaging session for more directinvestigation or immediate treatment.

These and other benefits may become clearer upon making a thoroughreview and study of the following detailed description. Referring now tothe drawings, and in particular to FIG. 1, an illustrative steerablecapsule 100 apparatus for maneuvering within a small space includes amain body 105 with at least one tail 110 connected to the main body 105such that the at least one tail 110 extends distally from the main body105. At least two coils 115, 120, and 125 are disposed on each tail 110such that the coils 115, 120, and 125 are responsive to a magnetic fieldinteracting with the coils. The interactions with the magnetic fieldresult in a force exerted on the tail(s) 110.

A control circuit, also referred to as a driving circuit 130,communicates with the coils 115, 120, and 125 to provide a current tothe coils to affect interaction with the magnetic field and to controlthe forces exerted on the tail(s) 110. The driving circuit 130 cancomprise a fixed-purpose hard-wired platform or can comprise a partiallyor wholly programmable platform to perform the controlling and drivingmethods described herein. All of these architectural options are wellknown and understood in the art and require no further description here.A power source 140, such as a battery, may be included in the capsule100, or the capsule 100 may be powered through currents generated in thecoils 115, 120, 125 by externally applied magnetic fields. The controlor driving circuitry 130 or separate circuitry can be configured by oneskilled in the art to control the collection and provision of such powerin the capsule 100.

Motion is generated for the capsule 100 by placing a conductive element,here the coils 115, 120, and 125, carrying electric current into astatic magnetic field B₀, as may be applied, for example, by an MRIdevice. The interaction between the current carrying element and themagnetic field creates a force on the current carrying element. Byalternating the direction of the current in the coils 115, 120, and 125or by varying a magnetic field applied to the coils 115, 120, and 125, aback and forth type of force and motion may be created. The LorentzForce Law, having the equation F=q(E+v x B), describes the force F,exerted on the charged particles moving in the coils 115, 120, and 125in the presence of electric and magnetic fields.

For this force equation, q is the charge of the particle, v is the speedof the particle, E is the electric field intensity felt by the particle,and B (B=μ₀H) is the magnetic field intensity felt by the particle.Because the current created by the charged particles needs to form aclosed loop to flow, the force F acts along the current path of theconductive wire loop forming the coils 115, 120, and 125. Diagrams ofsimilar coils 205 and 210 with indications of the forces F, charge iflowing through the coils 205 and 210, and applied magnetic field B₀ areillustrated in FIG. 2. In these coils, a magnetic field is created whenthe charge or current i flows circularly through the coils. The magneticfield created by the current flow experiences a force tending to alignwith the external magnetic field B₀. Accordingly, the coil 205 that isin line with the magnetic field B₀ experiences a force F tending torotate the coil 205 such that it ends up perpendicular to the magneticfield B₀, as shown in coil 210. The forces F experienced by the coil 210cancel each other such that the coil 210 remains substantiallyperpendicular to the applied magnetic field B_(0 .)

With reference to FIG. 1, such forces can be used in one approach tocontrolling movement of the capsule 100 in a fluid or small spaceenvironment. A current is provided to the coils 115, 120, 125 disposedon the tail(s) 110 coupled to a main body 105 of the capsule 100. Thecurrent is controlled so as to control interaction between the coils115, 120, 125 and a magnetic field applied to the coils 115, 120, 125.The current can be varied to affect varying forces on the coils 115,120, 125 to affect bending of each tail 100 having coils 115, 120, 125receiving the current. By another approach, a substantially constantcurrent is provided to the coils 115, 120, 125 to affect interactionbetween coils 115, 120, 125 receiving the current and the magnetic fieldapplied to the coils 115, 120, 125. For example, the capsule 100 may berotated without lateral movement by applying a constant current to thecoils 115, 120, and 125 and wherein the applied magnetic field is aconstant magnetic field that aligns the capsule 100 with respect to theconstant magnetic field. The constant current in combination with theapplied magnetic field B₀ creates a torque on the coils 115, 120, and125 as described above with reference to FIG. 2, thereby turning theentire capsule 100 in such a way that the axis (normal) of the coilstends to be aligned with the direction of the static magnetic field B₀.

To generate a propulsive force, at least two coils 115, 120, and 125 areplaced on an elongated tail 110, and the capsule 100 having the tail 110is surrounded with fluid. Each of the coils 115, 120, and 125 is drivenby a current with each coil's current having a particular sinusoidalwaveform crafted for propulsive force. The current with a sinusoidalwaveform can be created by the control or driving circuitry 130 in thecapsule 100 or by the coils' interaction with external varying magneticfields applied to the capsule 100 by external devices, such as an MRImachine or other magnetic field generator(s). The waveform amplitude andthe phase may be different for each coil 115, 120, and 125, while thefrequencies for the coils 115, 120, and 125 may have the same value. Theinteraction between the static magnetic field B₀ applied from outsidethe capsule 100 and the current flowing in the coils 115, 120, and 125creates a time and location dependent bending along the tail 110. Thephases and amplitudes of the waveforms are optimized to create atraveling wave in the tail 110. This traveling wave exerts a propulsiveforce on the fluid surrounding the tail 110 and creates linear forwardmotion for the capsule 100. This propulsion method is able to move apayload in the direction of the static magnetic field of the MRI, whichis difficult to achieve with different propulsion methods.

A capsule 100 with a single tail 110 as shown in FIG. 1 is able to movein one direction. To maneuver in a two-dimensional plane, two tails arenecessary, and to move in a three-dimensional space at least three tailsare needed as shown for example in FIG. 3. Each tail in theseembodiments provides substantially forward propulsion; therefore, bydriving all three tails 310, 320, and 330 with the same signal, thecapsule 340 will advance in the Z direction. Applying differentamplitude signals for each tail 310, 320, and 330 enables advancing andturning into any direction.

By one approach to controlling the propulsion, with reference again toFIG. 1, an MRI machine may apply the external magnetic fields. Duringthe operation of an MRI, two kinds of magnetic fields are introducedinto the region in addition to the static magnetic field across theregion. One of the fields is a gradient magnetic field; the other is aradio frequency (“RF”) magnetic field. Because these magnetic fields arechanging in time, they induce a current in the coils 115, 120, and 125.Faraday's Induction Law describes the relationship between the electricfield E driving the current in the coils and the magnetic field B:

${\oint\limits_{L}{Edl}} = {\frac{\partial}{\partial t}{\int_{A}{B\ {A}}}}$

The line L encloses the surface area A of each coil 115, 120, and 125.This equation shows that the varying magnetic fields applied to thecapsule 100 will induce varying currents in the coil 115, 120, and 125.Accordingly, a varying magnetic field can induces a varying current inthe at least two coils, and at least one of the coils can be connectedto the main body 105 such that the current provides power to at least aportion of the main body 105. For example, the driving circuitry 130 canbe powered by the current such that the driving circuitry 130 controlsthe tail 110. In one approach, the sinusoidal time varying nature of theRF magnetic field can be a power source for the capsule 100 because theRF signal can induce a varying electric current in the coils 115, 120,and 125 that can power the capsule 100 using circuitry known to thoseskilled in the art connected to the coils 115, 120, and 125 to rectifythe induced current and redistribute that energy in the capsule 100.Additional coils may be provided perpendicular to the coils 115, 120,125 such that power is still provided by the external magnetic fieldwhen the field is in the same plane as the coils 115, 120, 125. When itis not practical to utilize an MRI sourced RF magnetic field as a powersource, a similar external varying magnetic field may be substituted. Byanother approach to powering the capsule 100, batteries 140 may beincluded in the capsule 100. For example, standard hearing aid batteriescan be incorporated into the capsule 100.

The induced electromotive force EMF on a coil having a surface area Aand number of turns N from a magnetic field B having a frequency ω canbe described with the following equation:

${E\; M\; F} = {{- {NAB}}\frac{\partial}{\partial t}{{\sin \left( {\omega \; t} \right)}.}}$

When the coil has an electric load forming a closed electric circuit oftotal electrical resistance R, an electric current i will flow in thecoil in reaction to the applied magnetic field according to thefollowing equation:

${Ri} = {{E\; M\; F} = {{- {NAB}}\frac{\partial}{\partial t}{{\sin \left( {\omega \; t} \right)}.}}}$

The current created in the coil may then be utilized for propulsivepurpose. In this approach, the externally applied magnetic fieldcomprises a sinusoidal-varying magnetic field that induces a variablecurrent in the at least two coils that induces varying deformationsubstantially in accordance with a sinusoidal waveform in the at leastone tail. In this approach, the current in the coils can remain constantwhere the varying current is applied by the external magnetic field. Ina variation on this approach, the driving circuitry can vary theresistive load on the coil to create the right amount of current flow inreaction to the applied field.

By another approach, the applied magnetic field may be static, and thedriving circuitry is configured to provide a varying current to the atleast two coils such that the interaction with the magnetic fieldaffects varying forces on the at least one tail and varying deformationin the at least one tail. Here, the sinusoidal variation can becontrolled and applied by the driving circuitry instead of by thecontrols of the externally applied magnetic field, such as from an MRIdevice. By any of these approaches, the forces applied to the coils 115,120, and 125 can move or flex the tail 110 portions in a wave-likemanner to promote movement of the capsule 100.

One approach to calculating the frequency and current ranges for thecoils 115, 120, and 125 and the applied magnetic fields to affectpropulsion will now be described. Due to scaling effects in thehydrodynamic equations that describe how the capsule 100 travels in afluid, the swimming action in the micro world is different from macrosize swimmers. In fluid mechanics and aerodynamics, the Reynolds numberis a measure of the ratio of inertial forces to viscous forces, andconsequently, it quantifies the relative importance of these two typesof forces for given flow conditions. In micro flows that form thetypical environment for the capsule 100, the Reynolds numbers are low(Re<1) thereby enabling the omission of the inertial terms from theNavier-Stokes equations and confining the equations to the viscous flowenvironment. In addition, the linearity of the Stokes equations in theviscous flow environment generally prohibits the use of repeated motionsuch as that of the fish tail in the micro-mechanism to generatepropulsion force. Swimming in the viscous flow is achievable insteadthrough undulatory action. Following a known theoretical model andinspired by the flagellar movement of microorganisms, the oscillatingbeam of the tail 110 can create an approximated sinusoidal travelingwave in viscous flow and produces propulsion force effectively. Thesinusoidal wave from the tail 110 can be described with the followingequation:

$\begin{matrix}{{w^{(d)}\left( {x,t} \right)} = {w\; \sin \; {\kappa \left( {x - {Ut}} \right)}}} \\{= {{w\left( {{\sin \; \kappa \; x\; \cos \; \kappa \; {Ut}} - {\cos \; \kappa \; x\; \sin \; \kappa \; {Ut}}} \right)} =}} \\{= {\sum\limits_{k = 1}^{\infty}{\left( {{{Cs}_{k}\cos \; \kappa \; {Ut}} - {{Cc}_{k}\sin \; \kappa \; {Ut}}} \right){\varphi_{k}(x)}}}} \\{= \; {{\sum\limits_{k = 1}^{\infty}{{g_{k}^{(d)}(t)}{\varphi_{k}(x)}}} \approx {\sum\limits_{k = 1}^{3}{G_{k}{\sin \left( {{\Omega \; t} - \Phi_{k}} \right)}{\varphi_{k}(x)}}}}}\end{matrix}$

where w, k, and U are respectively the amplitude, wave number, and wavevelocity of the desired advancing wave in the tail 110. Cs_(k) andCc_(k) are the decomposition of sin kx and cos kx into the modalfunctions, φ_(k)(x), of the k-th mode of the tail. The function g_(k)^((d))(t) is the desired time function of the k-th mode to be achievedin the tail 110 to affect the desired traveling wave w^((d))(x,t).

These equations may be extended to an elongated tail 110 with multiplecoils 115, 120, and 125 attached in a row. The number of coils 115, 120,and 125 in a tail 110 is equal to the number of controllable timefunctions g_(k) ^((d))(t). At least two coils 115, 120, and 125 areneeded to create undulatory motion in the tail 110. Using a large numberof coils 115, 120, and 125 increases the driving frequency but can addadditional technological difficulties. One approach illustrated in FIG.1 includes using three coils 115, 120, and 125 in a row for the swimmingtail 110. To create the phases Φ_(k) and amplitudes G_(k), one has totake into consideration the tail's dynamical response. Accordingly, theabove equation can be solved to determine the input currents that cancreate the amplitudes {G₁, G₂, G₃} and phases {Φ₁Φ₂Φ₃} for the aboveequation that will cause the tail 110 to vibrate in a sinusoidaltraveling wave.

The tail's vibration can be divided into three segments corresponding tothe coils 115, 120, and 125 on the tail 110: w_(l)(x,t) is the lateralmotion of the tail 110 in the area bounded by the coil 115 closest tothe main body 105 defined by x=[0,α₁L]; w₂(x,t) is the lateral motion atthe middle coil 120 where x=[α₁L, α₂L]; and w₃(x,t) is the lateralmotion at the coil 125 therein the end of the tail 110 where x=[α₂L,L].The motion of the tail 110 is governed by the Euler-Bernoulli beamequations:

${{m_{1}\frac{\partial^{2}{w_{1}\left( {x,t} \right)}}{\partial t^{2}}} + {c\frac{\partial{w_{1}\left( {x,t} \right)}}{\partial t}} + {{\overset{\Cap}{K}}_{1}\frac{\partial^{4}{w_{1}\left( {x,t} \right)}}{\partial x^{4}}}} = {{0{\forall x}} = \left\lbrack {0,{\alpha_{1}L}} \right\rbrack}$${{m_{2}\frac{\partial^{2}{w_{2}\left( {x,t} \right)}}{\partial t^{2}}} + {c\frac{\partial{w_{1}\left( {x,t} \right)}}{\partial t}} + {{\overset{\Cap}{K}}_{2}\frac{\partial^{4}{w_{2}\left( {x,t} \right)}}{\partial x^{4}}}} = {{0{\forall x}} = \left\lbrack {{\alpha_{1}L},{\alpha_{2}L}} \right\rbrack}$${{m_{3}\frac{\partial^{2}{w_{3}\left( {x,t} \right)}}{\partial t^{2}}} + {c\frac{\partial{w_{1}\left( {x,t} \right)}}{\partial t}} + {{\overset{\Cap}{K}}_{3}\frac{\partial^{4}{w_{3}\left( {x,t} \right)}}{\partial x^{4}}}} = {{0{\forall x}} = \left\lbrack {{\alpha_{2}L},L} \right\rbrack}$

where m_(i) is the distributed mass of each tail 110 segment, c is thedamping coefficient and K₁ is the elastic stiffness of each segment. Thedefinition for each of these elements is known.

The boundary conditions of the tail 110 then can be described with thefollowing equations:

${{at}\mspace{14mu} x} = {{0\text{:}\overset{\Cap}{\mspace{14mu} K_{1}}\frac{\partial^{2}{w_{1}\left( {0,t} \right)}}{\partial x^{2}}} = {{- K_{\theta}}\frac{\partial{w_{1}\left( {0,t} \right)}}{\partial x}\mspace{14mu} {and}}}$${{\overset{\Cap}{K_{1}}\frac{\partial^{3}{w_{1}\left( {0,t} \right)}}{\partial x^{3}}} = {{- {{Kw}_{1}\left( {0,t} \right)}} + {F_{L\; 1}(t)}}};{and}$${{at}\mspace{14mu} x} = {{L\text{:}\mspace{14mu} \frac{\partial^{2}{w_{3}\left( {0,t} \right)}}{\partial x^{2}}} = {0\mspace{14mu} {and}}}$${\overset{\Cap}{K_{3}}\frac{\partial^{3}{w_{3}\left( {0,t} \right)}}{\partial x^{3}}} = {- F_{L\; 3}}$

where K_(θ) is the spring coefficient of an angular spring located atthe base of the tail 110 and K is the coefficient of a linear springlocated at the base of the tail 110. K_(θ) and K were added to thetheoretical formulation to overcome the uncertainty of the tail clampingfor the capsula 100, and they are calibrated empirically. The Lorenzforce created by the magnetic field is described by the equation F_(Li)(t)=N_(i)b_(i)I_(i)(t)B₀ where B₀ is the magnetic field, N_(i) is thenumber of turns in the i-th coil, B_(i) is the width of the coil, andI_(i)(t) is the current in the coil.

The continuity conditions at the boundaries between two coils are thendescribed by the following:

at x=α₁L between coil 115 and coil 120:

w₁(α_(1 )L, t) = w₂(α₁L, t)${\overset{\Cap}{K_{1}}\frac{\partial^{2}{w_{1}\left( {{\alpha_{1}L},t} \right)}}{\partial x^{2}}} = {\overset{\Cap}{K_{2}}\frac{\partial^{2}{w_{2}\left( {{\alpha_{1}L},t} \right)}}{\partial x^{2}}}$${{\overset{\Cap}{K_{1}}\frac{\partial^{3}{w_{1}\left( {{\alpha_{1}L},t} \right)}}{\partial x^{3}}} + {F_{L\; 1}(t)}} = {{\overset{\Cap}{K_{2}}\frac{\partial^{3}{w_{2}\left( {{\alpha_{1}L},t} \right)}}{\partial x^{3}}} + {F_{L\; 2}(t)}}$

and at x=α₂L between coil 120 and coil 125:

w₂(α_(1 )L, t) = w₃(α₁L, t)$\frac{\partial{w_{2}\left( {{\alpha_{2}L},t} \right)}}{\partial x} = \frac{\partial{w_{3}\left( {{\alpha_{2}L},t} \right)}}{\partial x}$${\overset{\Cap}{K_{2}}\frac{\partial^{2}{w_{2}\left( {{\alpha_{2}L},t} \right)}}{\partial x^{2}}} = {\overset{\Cap}{K_{3}}\frac{\partial^{2}{w_{3}\left( {{\alpha_{2}L},t} \right)}}{\partial x^{2}}}$${{\overset{\Cap}{K_{2}}\frac{\partial^{3}{w_{2}\left( {{\alpha_{2}L},t} \right)}}{\partial x^{3}}} + {F_{L\; 2}(t)}} = {{\overset{\Cap}{K_{3}}\frac{\partial^{3}{w_{3}\left( {{\alpha_{2}L},t} \right)}}{\partial x^{3}}} + {F_{L\; 3}(t)}}$

To solve the above equations by a separation of variables method, onehas to convert the boundary conditions. The conversion will result in aset of polynomials in the field equation and homogeneous boundary andcontinuity conditions. The solution of the problem has the followingform:

${{w_{i}\left( {x,t} \right)} = {{\sum\limits_{k = 1}^{\infty}\; {{\varphi_{k}^{(i)}(x)}{g_{k}(t)}{\forall i}}} = 1}},2,3$

In this solution, φ_(k) ^((i))(x) is the shape of the k-th modalfunction in the tail segment i, and g_(k)(t) is the time function of thek-th mode of the tail 110. In the converted problem, the modes and thenatural frequencies are found, and the partial differential equationsfor the boundary conditions are converted to an infinite set of ordinarydifferential equations with one differential equation for each mode. Theordinary differential equations are already presented in the Laplaces-domain because the steady state solution of problem provides theinformation needed for operating the tail 110. The general form of thetime function is:

${{g_{k}(s)} = {{{- \begin{pmatrix}{1 + \frac{s\left( {s + {2\xi_{k}^{(1)}\omega_{k}}} \right)}{s^{2} + {2\xi_{k}^{(1)}\omega_{k}s} + \omega_{k}^{2}} +} \\{\frac{s\left( {s + {2\xi_{k}^{(2)}\omega_{k}}} \right)}{s^{2} + {2\xi_{k}^{(2)}\omega_{k}s} + \omega_{k}^{2}} +} \\\frac{s\left( {s + {2\xi_{k}^{(3)}\omega_{k}}} \right)}{s^{2} + {2\xi_{k}^{(3)}\omega_{k}s} + \omega_{k}^{2}}\end{pmatrix}}{\sum\limits_{i = 1}^{3}\; {{Cp}_{k}^{(i)}{F_{Li}(s)}{\forall k}}}} = 1}},2,\ldots \mspace{14mu},\infty$

The function ξ_(k) ^((i)∀k=)1, 2, . . . , ∞ is the damping ratio in thei-th segment of the k-th mode, ω_(k) is the natural frequency of thek-th mode, and Cp_(k) ^((i)) is the decomposition of the polynomial thatwas used to convert the problem in the earlier steps of the solution.

Because there are three inputs to the system u=[Fu(s), Fu(s),F_(L1)(s)]^(T), a three-time function can be controlled y=[g₁(s), g₂(s),g₃(s)]^(T). The above time function is truncated at the third mode for athree coil system to create a three by three square multipleinput-multiple output system, y=P(s)u. From the transfer matrix, P(s),an input u can be found that gives the desired output, y=[g₁^((d))(s),g₂ ^((d))(s),g₃ ^((d))(s)]^(T) and activates the tail 110 byopen loop control. Further details on the calculation of the amplitudes{G₁, G₂, G₃} and phases {Φ₁Φ₂, Φ₃} are known and available in thearticle Kósa, G., Shoham, M. and Zaaroor M., Propulsion of a SwimmingMirco Medical Robot, IEEE Conference on Robotics and Automation(ICRA05), (2005) 1339-1343, which is incorporated in its entiretyherein. The above equations can be readily implemented in software orfirmware in the capsule circuitry and/or in the external magnetic fieldgenerators to control the application of magnetic fields and/or currentto the coils 115, 120, and 125 to control the movement of the tail 110.FIG. 4 illustrates a simulation of the motion created in the tail 110 bythe input forces calculated from the above multiple input-multipleoutput system based on the equation for g_(k)(s) above.

More specifically, in one approach, the patient or subject swallows thecapsule, and a gastroenterologist maneuvers it using magnetic fieldsgenerated by an MRI device in combination with MRI imaging guidance,monitoring, and/or mapping. The capsule can be extremely small and haveno attached tethering. For example, a capsule built according to theseteachings can range in size between about 3 and about 30 millimeters inlength and between about 3 and about 15 millimeters in diameter,depending on the payload or tools carried in the capsule. Example toolsthat may be carried in the capsule include a small camera, a biopsytool, a small container in combination with a micro pump and a microvalve, a communication device, an electrode, and at least one operatingtool. Such micro-sized cameras and communication devices are known andavailable commercially. In one example combination, a camera,communication device, and power source can be disposed in a main body ofthe capsule with a size of about 11 millimeters in diameter and 27millimeters in length. In another example, a camera having a size of 3.5millimeters in diameter and 12 millimeters in length can be disposed inthe main body of the capsule.

With reference to FIG. 3, in another example, a capsule 340 includes acamera 345 and three tails 310, 320, and 330 connected to the main body305, each tail having a 10 millimeter length, 1.5 millimeter width, and0.15 millimeter thickness (about 0.2 millimeter including the coils). Inthis example, each tail 310, 320, 330 comprises a polymer film withcopper wire coils 350, 355, 360 secured to the film using acetone. Thethree tails 310, 320, 330 extend from the mail body essentiallyequidistantly from each other. By one approach, the coils may include afirst coil 350 of wire having a first number of turns and a firstsurface area such that the first coil 350 has a first resonant frequencyand a second coil 355 of wire having a second number of turns and asecond surface area such that the second coil 355 has a second resonantfrequency. In another approach, the wire may be printed on to the tailbody. In the example of FIG. 3, each coil 350, 355, 360 includes 4 rowsof 25 turns of wire for a total of 100 turns. The wire is a copper wireof American Wire Gauge 48 (0.0012 inch or 0.0315 millimeter diameter).The coils 350, 355, 360 have lengths of 2.0 millimeters, 3.7millimeters, and 4.3 millimeters, respectively. According to thecalculations above, the natural resonant frequencies for the coils 350,355, 360 are 294 Hertz (“HZ”), 4.036 kHz, and 12.836 kHz. The thirdorder frequency, 12.836 kHz, is applied to the capsule 340 by an MMdevice to drive the coils 350, 355, 360.

The driving circuitry 370 of the capsule 340 is configured to providecurrent of 10 milliamps to the coils 350, 355, 360. The drivingcircuitry 370 in this example is powered by a separate coil 380 thatpicks up the energy from the RF magnetic field of the MRI device topower the capsule 340. The coils 350, 355, 360 interact with a staticmagnetic field of 1 Tesla and an oscillating magnetic field applied bythe MRI device to create a propulsion force of 0.04 milli-Newton. Usingthe MRI's magnetic field to wirelessly send energy and generatepropulsion force, the capsule 340 will steer itself under the directionof the magnetic field and reach a suspected lesion and perform detaileddiagnostic examination. When the capsule 340 is confined to a narrowcavity and the tail(s) contacts the surface of the cavity, an additionalstick-slip mechanism comes into action, and the propulsion parallel tothe cavity wall can increase significantly.

When the MM device is used to control the capsule, additionalfunctionality can be provided to the system. In addition to providingthe magnetic field that engages the coils to affect movement of thecapsule, one can capture an image of the cavity including the capsule.Then, the system can mark a portion of the image with a location of thesteerable capsule relative to the cavity. The image of the cavity can becreated using the MRI device.

So configured, use of MRI can control the movement of such capsules in acavity and localize the swimming-robot in cross-sectional images. Thishelps maneuver the capsule toward the target organ in a shorter time andreduce the overall examination time. The ability to use the MRI tomaneuver the capsule arises because no ferro-magnetic material need beincorporated into the capsule. In contrast to prior legged capsules, thedescribed design is relatively simple and easy to fabricate, and thetails do not require large motion to cause movement. The propulsiveforce is instead generated by multiple high frequency (12 kHz)sinusoidal signals having phase differences that create the travelingwave in the swimming tails. In addition, the high vibration frequencymay prevent adhesion to the cavity walls, such as in an intestine.

Those skilled in the art will recognize that a wide variety ofmodifications, alterations, and combinations can be made with respect tothe above described embodiments without departing from the spirit andscope of the invention. For example, alternative approaches can utilizealternative magnetic field sources. In another example modification, asillustrated in FIG. 5, one or more of the tails 510 and 515 of thecapsule 500 can be disposed proximate to the main body 505 wherein thetail(s) 510 and 515 extends along the main body 505 of the capsule 500instead of extending from a distal end of the capsule 500.

Such modifications, alterations, and combinations are to be viewed asbeing within the ambit of the inventive concept.

1. A swimming capsule for navigation in a cavity comprising: a mainbody; at least one tail connected to the main body; at least two coilsdisposed on each tail such that the at least two coils are responsive toa magnetic field interacting with the at least two coils such that aforce is exerted on the at least one tail; a driving circuitcommunicating with the at least two coils to provide current to the atleast two coils to affect interaction with the magnetic field andcontrol the forces exerted on the at least one tail.
 2. The capsule ofclaim 1 wherein the main body comprises at least one of a groupcomprising: a small camera; a biopsy tool; a small container incombination with a micro pump and a micro valve; a communication device;an electrode; and at least one operating tool.
 3. The capsule of claim 1wherein the at least one tail comprises three tails connected to themain body.
 4. The capsule of claim 3 wherein the three tails extend fromthe main body essentially equidistantly from each other.
 5. The capsuleof claim 1 wherein the at least one tail comprises at least in part apolymer film.
 6. The capsule of claim 1 wherein the at least one tailextends distally from the main body.
 7. The capsule of claim 1 whereinthe at least one tail is disposed proximate to the main body.
 8. Thecapsule of claim 1 wherein the at least two coils comprise a first coilof wire having a first number of turns and a first surface area suchthat the first coil has a first resonant frequency; a second coil ofwire having a second number of turns and a second surface area such thatthe second coil has a second resonant frequency.
 9. The capsule of claim1 wherein a magnetic resonance imaging device provides the magneticfield.
 10. The capsule of claim 1 wherein the magnetic field comprises aconstant magnetic field that aligns the capsule with respect to theconstant magnetic field.
 11. The capsule of claim 1 wherein the magneticfield comprises a varying magnetic field that induces a varying currentin the at least two coils, and at least one of the at least two coils isconnected to the main body such that the current provides power to atleast a portion of the main body.
 12. The capsule of claim 11 whereinthe driving circuitry is powered by the current such that the drivingcircuitry controls the at least one tail.
 13. The capsule of claim 1wherein the magnetic field comprises a sinusoidal-varying magnetic fieldthat induces a variable current in the at least two coils that inducesvarying deformation substantially in accordance with a sinusoidalwaveform in the at least one tail.
 14. The capsule of claim 1 whereinthe driving circuitry is configured to provide a varying current to theat least two coils such that the interaction with the magnetic fieldaffects varying forces on the at least one tail and varying deformationin the at least one tail.
 15. The capsule of claim 1 wherein the forceexerted on the at least one tail flexes the at least one tail.
 16. Amethod comprising: providing a steerable capsule comprising: a mainbody; at least one tail coupled to the main body; at least two coilsdisposed on each tail; disposing the steerable capsule in a cavity;providing a magnetic field that engages the at least two coils to affectmovement of the steerable capsule.
 17. The method of claim 16 whereinproviding the magnetic field that engages the at least two coils toaffect movement of the steerable capsule further comprises providing aconstant magnetic field that aligns the steerable capsule with respectto the constant magnetic field.
 18. The method of claim 16 whereinproviding the magnetic field that engages the at least two coils toaffect movement of the steerable capsule further comprises providing avarying magnetic field that induces a current in the at least two coils.19. The method of claim 18 wherein at least one of the coils isconnected to the main body such that the current provides power to atleast a portion of the main body.
 20. The method of claim 16 whereinproviding the magnetic field that engages the at least two coils toaffect movement of the steerable capsule further comprises providing asinusoidal-varying magnetic field that induces a variable current in theat least two coils that induces varying deformation substantially inaccordance with a sinusoidal waveform in the at least one tail.
 21. Themethod of claim 16 further comprising: capturing an image of the cavity;marking a portion of the image with a location of the steerable capsulerelative to the cavity.
 22. The method of claim 21 wherein capturing animage of the cavity further comprises taking an image of the cavityusing a magnetic resonance imaging device.
 23. A method of controllingmovement of a capsule in a fluid or small space environment comprising:providing a current to at least two coils disposed on at least one tailcoupled to a main body of the capsule; controlling the current so as tocontrol interaction between the at least two coils and a magnetic fieldapplied to the coils.
 24. The method of claim 23 wherein the step ofcontrolling the current further comprises varying the current to affectvarying forces on the at least two coils to affect bending of each tailhaving coils receiving the current.
 25. The method of claim 23 whereinthe step of controlling the current further comprises providing asubstantially constant current to the at least two coils to affectinteraction between coils receiving the current and the magnetic fieldapplied to the coils.